Not really specific to derby but I typically find it easier to store the file name as a string in the DB and use code to find the file on the file system. Dunno if that fits your requirements. Good luck.
the maximum size of a table is the maximum file size of the underlying operating system (e.g.: 2 GB).
For data with a size of 10 MB I would reach the limit with about 200 entries.
The data once in the table needs only be read (attachments of messages). Perhaps the new table function can be used to show the content of the filesystem as a table, when the attachments are stored outside of the database.
Is there a way to distribute a table over more than one file or another solution?
Any solution is appreciated!